We asked internal sources at Facebook, as well as external executives at Facebook's client companies, to tell us what they knew about Facebook's top spenders. Our friends at ComScore also supplied us with some incredibly useful information about ad impressions served in social media. We also looked at previously published reports about ad spending on Facebook.

Combing that data together allowed us to rank the companies by dollars spent, for a period roughly covering the last 12 months.

Some of the results are surprising. Who knew, for instance, that cable TV company Turner probably spends more on Facebook ads than most other companies due to its heavy promotion of its channels, like CNN?

Others, less so. You can probably guess the No.1 biggest ad client of Facebook, if you think about it.

Our list has its flaws: Some key sources declined to cooperate with our survey, and we've doubtlessly missed some companies or gotten brand names ranked in the wrong order. Nonetheless, we're confident that our ranking is the best available outside of Facebook vp/global marketing solutions Carolyn Everson's office. (And you can email us if you have better information that could make this list more accurate.)

Stay tuned: On Thursday, when BI's Social Media ROI conference kicks off, we'll publish a ranking of the biggest ad spenders in all of social media, not just Facebook. (Disclosure: The author owns Facebook stock.)

30. FORD defended Facebook when General Motors pulled its $10 million ad budget before the Facebook IPO.

Ford global sales and marketing vp Jim Farley told the Wall Street Journal this year he has deepened his use of Facebook: "Someone who 'likes' you on Facebook is substantially more willing to advocate the brand."

29. HSBC has a large Facebook footprint in Europe and Asia.

HSBC / Facebook

HSBC learned early that simply not being on Facebook can be a crisis management handicap when, in 2007, it was the target of a Facebook-based protest movement by British students angry that their interest-free overdrafts were being scrapped by the bank.

26. VISA has had a robust Facebook ad budget since at least 2008, the year in which it spent $2 million on a small business promotion.

"We threw down the gauntlet at an all-hands marketing meeting early on, that we will make this the most social games for us and for any other sponsor so far," said Kevin Burke, global CMO for core products.

25. MASTERCARD sees payments via Facebook as a huge opportunity.

But it is the payment/credit aspect of Facebook that most entices CEO Ajay Banga. He told Wall Street analysts this year that Facebook is a “huge opportunity”:

“I’m not surprised at all by their payments revenue, because how do you load the Facebook credit right now?” Banga said on MasterCard’s earnings call Thursday. “You do it through various ways, which includes our cards.”

24. NIKE sometimes breaks campaigns on Facebook before they appear on TV.

21. CITI has an advanced CRM effort on Facebook.

Facebook / Citi

Citibank sponsors so many different things — concerts, the arts, charities — that its Facebook page is incredibly busy. It's also one of Citi's main CRM channels: Disgruntled customers get quick answers from the bank's social media staff.

20. STARBUCKS knows its customers are often checking Facebook when they're sitting in its cafes.

Facebook users who saw Starbucks messaging in their newsfeed saw a 38 percent “lift” in the purchase frequency – that is, visiting a store and buying something — over users who didn’t see the ads. The results showed up in the four weeks after users saw their first ads, and increased over time.

19. L'OREAL works with Salesforce to communicate with salons that use its products.

13. EBAY uses apps to tie its business to Facebook's

Ebay / Facebook

EBay has a partnership with Facebook which integrates Facebook’s Open Graph global commerce platforms. It's intended to encourage developers to create eBay apps on Facebook that will generate more business for the auction site.

12. VERIZON'S customers can access Facebook through their TVs.

Verizon / Facebook

Verizon has done some huge fanning campaigns by offering free exclusive TV content via FIOS for Facebook fans only, such as this Green Day concert.

FIOS has also had a Facebook widget -- which TV watchers can call up and use on-screen -- for years.

9. WALMART doesn't just have a Facebook page, 3,896 of its stores have one too.

Walmart / Facebook

One of its Facebook promotions made headlines earlier this year when it offered to send the performer Pitbull to the Walmart store that received the most likes from shoppers. The contest was hijacked by trolls, who liked Walmart's remote Kodiak, Alaska, store 70,000 times. Pitbull and Walmart honored the result anyway, and Pitbull bought some bear repellent (and enjoyed the headlines).

8. GROUPON uses AdParlor to handle its Facebook advertising spend.

A photo of Groupon HR staffers Gina and Tim (no last names given) that the company posted on its Facebook page.Groupon / Facebook

The Groupon/AdParlor "exclusive contract represents tens of millions of dollars in spend, as Groupon uses Facebook ads extensively to drive email signups and sell daily deals," according to InsideFacebook.

6. AMERICAN EXPRESS has gone all out on Facebook.

American Express / Facebook

American Express is incredibly advanced in online, social and mobile media generally.

Amex made a Facebook app called “Link, Like, Love,” in which cardholders link their cards to their Facebook accounts. In return they get deals from Whole Foods, Dunkin’ Donuts, Virgin America, and Sports Authority, among others. (The LLL app is separate to Facebook's official Offers deal function.)

5. AT&T's CEO regards Facebook as a "major force" in his universe.

Facebook / AT&T

AT&T CEO Ralph de la Vega once said of Facebook, “I think that social networking is going to be a major force in this industry for years to come ... I think it helps people communicate. That’s what we do.”

More importantly, Facebook's mobile app is one of the most ubiquitous and most-used apps on any phone; frequently it's Facebook, not a call or a text, that's the reason people pick up their phones.

The company has also run a sustained effort against texting and driving.

4. PROCTER & GAMBLE thinks it can generate $500 million in sales from Facebook and other social media.

Facebook / P&G

Famously, P&G began cutting its traditional media budget as a proportion of sales after CEO Bob McDonald told Wall Street he realized free viral exposure on Facebook was more efficient than than the brute-force buying of ratings points on TV.